1. Field of the Invention
This invention relates to a target for use in a photogrammetric analytical measurement system, in which a survey map is produced on the basis of a set of photographed pictures obtained at different photographing positions.
2. Description of the Related Art
For example, photogrammetry is carried out at a traffic accident spot. The traffic accident spot is photographed by a camera from at least two different positions, and a survey map of the traffic accident spot is produced, based on a set of photographed pictures obtained at the different positions. A target is placed in a photogrammetry spot, for example the above-mentioned traffic accident spot, in order to calculate positional data of the camera at which the pictures are photographed. The target includes three standard point members (indicating members). The three standard point members are made of a material of high luminance. Namely, an amount of incident light reflected from the material is increased to facilitate recognition of the standard point members in the photographed pictures.
The photogrammetry spot is photographed with the target by the camera at different positions and angles. The photographed images are converted to a plurality of digital image data which are stored in a memory of a computing system. A pair of digital image data are chosen from among the plurality of digital image data, and they are displayed on a monitor which is connected to the computing system.
A given measurement point is selected in one of the chosen pair of digital image data, and a corresponding measurement point is selected in another of the chosen pair of digital image data. The selection is carried out with a cursor by manipulating a mouse. This operation is repeatedly performed such that a plurality of pairs of measurement points are selected. A series of predetermined operations is carried out based on positional data of the above-mentioned standard points and the indicated measurement points, so that a survey map of the photogrammetry spot is produced.
Besides the positional data of the standard point members, data regarding positioning of the target is required for the predetermined operations, and therefore, the target for the above-mentioned photogrammetric analytical measurement system is provided with sensors, for example a tilt sensor, an azimuth sensor and so on. Information from these sensors is utilized to create the data regarding the position of the target. The data regarding the position of the target is transmitted to the camera during a photographing operation via an antenna which is provided in the target. After the data is received by the camera, the data is stored in a memory of a processor, which is included in the camera, with the photographed image data.
Usually, a predetermined distance exists between the target and the position of the camera, when the photogrammetry spot is photographed. Further, the target is situated on a surface of a road of the photogrammetry spot, and the camera is positioned at a predetermined height from the surface of the road. Accordingly, a rod antenna may be utilized to make the transmittance from the antenna to the camera highly sensitive.
However, as the rod antenna projects further than other components of the target, the rod antenna may be hit when it is carried, or may be kicked by mistake when it is set on the road. Namely, the rod antenna has a problem in that it is easy to be broken. Further, due to a positional relationship between the standard point members, the rod antenna and the position of the camera, the standard point members may be obstructed by the rod antenna, so that the standard point members may not be photographed. If the standard point members are not photographed, precise positional data of the standard point members can not be obtained, so that the above-mentioned operation for producing a survey map cannot be carried out.
Therefore, an object of the present invention is to provide a target for a photogrammetric analytical measurement system, including an antenna which transmits data to a camera reliably without obstructing any indicating members of the target.
In accordance with an aspect of the present invention, there is provided a target for photogrammetric analytic measurement comprising: a first bar and a second bar which are connected at adjacent end portions; indicating members that are able to be recognized in a photographed image by a camera, placed on the first and second bars to define an identical plane; a box in which sensors for detecting data utilized to calculate a photographing position of the camera, provided on the first bar or the second bar at a position close to the connecting end portion; a loop antenna that transmits the data detected by the sensors to an outer device; and a projecting portion in which the loop antenna is provided, being placed on the box, at a side at which the indicating members are placed, on the first and second bars. A relationship between a first distance and a second distance are defined by an expression to follow. The first distance is along the identical plane between a first indicating member of the indicating members, which is positioned close to the connecting end portion, and the projecting portion. The second distance is along a direction perpendicular to the identical plane between a top surface of the projecting portion and the identical plane. The expression is:
K2/K1 less than tan 8xc2x0
(herein, K1 is the first distance, K2 is the second distance)
Preferably, a total length of a conductor, which is wound to construct the loop antenna, is approximately half of a wavelength of a radio wave sent from the loop antenna. The inner diameter of the winding of the conductor is within a range between approximately 25 mm (millimeters) through 50 mm, and a distance, along the perpendicular direction, between the identical plane and the loop antenna is greater than or equal to approximately 8 mm.
Preferably, the projecting portion has a generally cylindrical configuration which is coaxial with a center axis of the loop antenna. The center axis exists on a bisector of the first indicating member and a second indicating member of the indicating members, which is placed on the first or second bar at which the box is provided, being adjacent to the first indicating member.
Optionally, the projecting portion comprises: a holding member that holds the loop antenna, being fixed on the top surface of the box; and a covering member that protects the loop antenna from the outer side.
Optionally, the projecting portion is fixed on the top surface of the box, being made of resin, and the loop antenna is molded in the projecting portion.
Preferably, the box is positioned at an area of a right angle or an acute angle made by the first and second bars.
As described above, according to the present invention, the data detected by the sensors is transmitted by the loop antenna. Accordingly, the size of the projecting portion in which the antenna is provided can be changed such that the projection above other components of the target, can be reduced. Further, the first indicating member is not obstructed by the antenna in a photographed image, by positioning the projecting portion on the box such that the first distance and the second distance satisfies the aforementioned expression.
Due to the reduction in size of the projecting portion, the projecting portion is prevented from being broken by carelessly hitting or kicking the projecting portion when the target is carried or set on a photogrammetric spot.
Further, according to the present invention, the total length of the conductor, which is wound to construct the loop antenna, is set to approximately half the a wavelength of a radio wave sent from the loop antenna, and the inner diameter of the conductor winding is set to a range between approximately 25 mm through 50 mm, and the distance, along the perpendicular direction, between the identical plane and the loop antenna is set to a value greater than or equal to approximately 8 mm. Therefore, a predetermined communication distance of the antenna can be obtained, so that data utilized for the photogrammetric analytic measurement can be reliably transmitted from the target to an outer device, for example a camera.